The present invention relates to a drilling system of the type defined in the preamble of claim 1 and to an associated prosthesis.
Cement-free prostheses are fixed in that a so-called press-fit situation is created. That means that the marrow region of the femur is shaped with the best possible precision so that a prosthesis of the correctly selected size for the respective femur can be hammered into the prepared marrow region with slight pressure. Adapting the marrow region to various prosthesis sizes is here possible only by means of a mechanical removal system. Removal with a conventional rasp, however, results in axial errors and, with great probability, produces a space which is too large in the proximal region, thus practically preprogramming the loosening of the prosthesis.
DE-AS No. 2,356,464 discloses a drill system as defined in the preamble of claim 1. The guide element which aligns the drill in an oblique position oriented toward the stem is displaceable in the associated drill gauge with respect to the stem-like shaft in the longitudinal direction of the latter. This displacement serves to completely cut out the prismatic region of the recess next to the cylindrical shaft so as to accommodate the corresponding part of the prosthesis. In its oblique position oriented toward the shaft, the cutter is brought toward the bone along a shaft which had previously been inserted into the bore until the cutter begins to widen the existing bore in the form of a triangular prism. If the obliquely directed cutter is advanced further, the prismatic region is excavated completely.
The drawback here is that the cutting takes place primarily along the sidelines of the cutter so that a force component (in the form of a bending moment) develops and bends the stem-like shaft, breaking it out of its guide in the bone. Moreover, the entire prismatic region must be removed by cutting, which in the course of surgery is a time-consuming process.